Multi-chip photosensor with independently adjustable integration times for each chip

ABSTRACT

A photosensitive apparatus, such as a scanner used in a digital copier, includes a plurality of photosensor chips. Each photosensor chip comprises a first set of photosensors, and a control portion for accepting an external integration signal, the signal causing an integration time for the set of photosensors. A signal adjustor is associated with the control portion, and effectively alters the external integration signal to cause the control portion to cause a modified integration time for the first set of photosensors. The system enables adjustments of integration times among chips within an apparatus sharing a common control line.

INCORPORATION BY REFERENCE

The following U.S. Patents are hereby incorporated by reference, intheir entireties, for the teachings therein: U.S. Pat. Nos. 5,519,514and 6,014,160; and Published Application 20060274174.

TECHNICAL FIELD

The present invention relates to image sensor arrays used in inputscanners, such as in digital copiers or facsimile machines, or indigital cameras.

BACKGROUND

Image sensor arrays typically comprise a linear array of photosensorswhich raster scan an image bearing document and convert the microscopicimage areas viewed by each photosensor to image signal charges.Following an integration period, the image signal charges are amplifiedand transferred as an analog video signal to a common output line or busthrough successively actuated multiplexing transistors.

For high-performance image sensor arrays, one possible design includesan array of photosensors of a width comparable to the width of a pagebeing scanned, to permit one-to-one imaging generally without the use ofreductive optics. In order to provide such a “full-width” array,however, relatively large silicon structures must be used to define thelarge number of photosensors. One technique to create such a large arrayis to make the array out of several butted silicon chips. In oneproposed design, an array is intended to be made of 20 silicon chips,butted end-to-end, each chip having active photosensors spaced at 400 ormore photosensors per inch.

Further, in a full-color scanner, as would be used in color copying,there may be provided three or more linear arrays on each chip, eacharray filtered to receive a single primary color. As described in U.S.Pat. No. 5,519,514, each linear array on a chip may be desired to beindependently controllable in some respects, particularly in terms of“integration time.” Integration time is, broadly speaking, the length aparticular photosensor is exposed to light from a small area on theoriginal image being scanned, to yield a pixel of data. In the case of acolor apparatus, each of three or more primary-color photosensors willview the substantially same small area in the original image, to yieldfull-color image data. In various situations, the integration timesassociated with different-color linear arrays on a single chip may bedesired to be finely adjusted.

The present disclosure addresses a system for adjusting integrationtimes associated with different photosensor sets in different chipswithin a larger system.

SUMMARY

According to one aspect, there is provided a photosensor chip comprisinga first set of photosensors, and a control portion for accepting anexternal integration signal, the signal causing an integration time forthe set of photosensors. A signal adjustor, associated with the controlportion, effectively alters the external integration signal to cause thecontrol portion to cause a modified integration time for the first setof photosensors.

According to another aspect, there is provided a photosensitiveapparatus, such as scanner used in a digital copier, includes aplurality of photosensor chips. Each photosensor chip comprises a firstset of photosensors, and a control portion for accepting an externalintegration signal, the signal causing an integration time for the setof photosensors. A signal adjustor associated with the control portioneffectively alters the external integration signal to cause the controlportion to cause a modified integration time for the first set ofphotosensors. A common line applies an external integration signal toeach of the plurality of photosensor chips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a portion of a “full-width-array” input scanneras would be used in office equipment such as a digital copier, as knownin the prior art.

FIG. 2 shows a photosensor chip 10 in isolation, as known in the priorart.

FIG. 3 is a simplified diagram illustrating a principle of the presentembodiment.

FIG. 4 and FIG. 5 are timing diagrams showing the operation of a signaladjustor among each of a set of chips, according to differentembodiments.

DETAILED DESCRIPTION

FIG. 1 is a plan view of a portion of a “full-width-array” input scanneras would be used in office equipment such as a digital copier. A set ofphotosensor chips, each indicated as 10, is arranged on a circuit board100. Each chip 10 includes a set of photosensors, as will be describedbelow. Together, the chips 10 on board 100 form one or more lineararrays of photosensors that extend a length comparable to the width ofan image-bearing sheet such as S effectively moving in a processdirection P. The sheet S can move relative to the board 100 by beingplaced on a platen (not shown) relative to which the board 100 moves; orthe sheet S can be fed through a document handler (not shown). As thesheet S moves past board 100, a series of small areas on the sheet Sreflect light (from a source, not shown) into photosensors on the chips10. The chips 10 receive the reflected light from sheet S and outputimage signals for subsequent recording and processing.

FIG. 2 shows a photosensor chip 10 in isolation. In this embodiment,each chip 10 includes four linear arrays, or rows, of photosensors,labeled 20M (for monochrome), 20R (for red), 20G (for green) and 20B(for blue). Each array is provided with a translucent filter (not shown)that causes the array to be sensitive to a particular color or range ofwavelength. The monochrome array 20M is sensitive to light throughoutthe visible spectrum, and is useful when scanning images formonochrome-only image data, as would be useful, for example, in amonochrome copier or facsimile machine, or for optical characterscanning. The photosensors may also be provided with other types offilters, such as for infrared blocking.

In the present embodiment, for each “column” (as shown in the Figure) ofone photosensor of each type 20M, 20R, 20G, 20B, there is one outputline to an output shift register 24. A general description of howmultiple photosensors in a column send signals over one line to a shiftregister is given in U.S. Pat. No. 5,148,168 mentioned above. It will beevident that each photosensor of each type 20M. 20R, 20G, 20B in acolumn will “look at” one small area of an image being recorded, toobtain full color image data about the small area. A description of howthe action of multiple photosensors of different colors must becoordinated is given in U.S. Pat. No. 5,519,514, mentioned above. Once a“scanline” of digital image signals is loaded into shift register 24,the image data for that scanline is output from the chip 10, such asthrough line V_(OUT).

As mentioned above, a key control for a chip 10 is the start and stoptimes defining an “integration time” of each photosensor. An integrationtime is the length of time a particular photosensor receives light froma given small area, typically as the sheet moves a series of small areaspast each photosensor. In a multi-chip system, it may be desirable tomake small adjustments in the integration time of a set of photosensorson the chip, such as to overcome manufacturing anomalies between chipswithin the same apparatus. As shown in the prior-art basic case in FIG.2, different lines for controlling the integration time of differentsubsets of photosensors, φFR, φFG, φFB (for red, green and blue rows ofphotosensors respectively) can feed into a control portion 26 governingthe chip 10.

FIG. 3 is a simplified diagram illustrating a principle of the presentembodiment. As with the previous Figures, a butted array of photosensorchips 10 is provided, each chip 10 a-z being connected through a commonline to an external control system (not shown). In the present case,each chip 10 a-z has at least three sets of photosensors thereon,typically a red-filtered, green-filtered, and a blue-filtered set. Eachset of photosensors on each chip, in turn, is controlled, in terms ofits integration time, by one external line, here marked φFR, φFG, φFB.In a basic case, a going-high signal on φFR would cause all redphotosensors on all chips to start an integration time, and going lowwould cause all red photosensors on all chips to end the integrationtime; the same principle applies to the green and blue photosensors withthe φFG and φFB. In this basic case, because all photosensors of eachcolor on each chip are controlled through a common line for theirintegrations times, there is no provision for chip-to-chip adjustmentsin integration times, should that be desired to overcome manufacturinganomalies between chips.

FIG. 3 further shows in detail a representative chip 10 n. At the inputlies for each external input φFR, φFG, φFB, there is provided what canbe called a “signal adjustor,” one for each color line, marked 30R, 30G,30B. The function of each signal adjustor is to effectively alter theincoming integration signal to cause a modified integration time for theset of photosensors. In an embodiment, each signal adjustor such as 30Raccepts the common input going simultaneously to all chips in thescanner; but, for the particular chip such as 10 n, outputs an alteredsignal which will have the effect of altering the integration time forthe red photosensors in some way. The altered signal is then fed intothe control portion 26, which uses the signal to control the integrationtime of the red photosensors in the same manner as in the basicprior-art case of FIG. 2.

One possible way the signal adjustor such as 30R can alter the incomingsignal φFR is to add or subtract from the duration of the signal(between going-high and going-low), by some predetermined amount. Theadjustment to the length of the incoming signal (to yield the modifiedsignal shown as φFR_(I)) will correspond to a change in the integrationtime for the red photosensors when the modified signal is applied to thecontrol portion 26. Other ways of adjusting the incoming signal couldinclude multiplying the duration of the signal by an adjustment constant(which may be more or less than 1.0); adjusting the amplitude of thesignal for whatever reason; or generating a new signal of predeterminedduration in response to receiving a change in state of the incomingsignal. (The present discussion, of course, applies to the φFG and φFBsignals as well, and the different sets of photosensors, controlled bydifferent input signals, can operate substantially independently withina chip such as 10 n.)

FIG. 4 and FIG. 5 are timing diagrams showing the operation of a signaladjustor such as 30R, among each of a set of chips 10 a-z, according todifferent embodiments. In the FIG. 4 embodiment, a generalized inputsignal φFX is modified in various ways by the signal adjustor ofdifferent chips, as indicated by φFX_(I)(a-z). As can be seen, variousof the modified signals φFX_(I)(a-z) are shorter or longer in duration,as required, compared to the input signal φFX; further, as can be seen,each modified signal φFX_(I)(a-z) is “centered” in time relative to theinput signal; i.e., a mandated longer signal starts before and endsafter the duration of the input signal, and a mandated shorter signalstarts after and ends before the duration of the input signal, so thatthe midpoints of the input signal and all the modified signals aresimultaneous. In an implementation of the FIG. 4 embodiment, the system“knows” when to start longer integration time signals (that wouldotherwise begin before the input signal), by learning thecharacteristics of an external clock with some counters and then makingadjustments to the counters. Another approach would be to determinemaximum integration time required for the sensor with the lowestresponse and then to adjust all of the others relative to this one sothey will all be shorter.

In the FIG. 5 embodiment, the system is designed so that the end pointsof all the modified signals are simultaneous with the endpoint of theinput signal. The FIG. 5 arrangement may be useful when coordinating theintegration times with readout circuitry (not shown), particularly inchip designs where video is output in response to a falling edge of aninput signal.

In one possible scenario, for a given chip 10, following manufacture andperhaps following installation into a larger, multi-chip apparatus, thesignal output from a particular set of photosensors on the chip ismeasured; and then a correction datum (such as an 8-bit word) is loadedinto the corresponding controlling signal adjustor such as 30R, 30B,30G, to cause subsequent outputs from the signal adjustor to change theintegration time of the set of photosensors to be consistent with astandard. In a practical implementation, loading of this correctiondatum is required only at manufacture of an apparatus such as a scanner,but in some scenarios, changing the correction datum to each signaladjustor on each chip in an apparatus over the course of use may bedesirable.

The above-described system, in which each set of photosensors on eachchip can be controlled by a modified signal within the chip, enableseach set of photosensors on each chip in a larger system to be finelyadjusted in terms of integration time. In a practical implementation,this adjustment of the integration times can be used to overcomemanufacturing anomalies among chips (and photosensor sets within achip), so that the amplitude of a video signal from all the sets ofphotosensors on all chips in an apparatus will be consistent.

In contrast with the present disclosure, a system of simply adjustinggain would not change the signal-to-noise ratio because any noise wouldalso be adjusted equally; and adjusting gain also adjusts offset, whichis not desirable. Changing the integration time, as in the presentdisclosure, is effectively the same as adjusting the light level on thephotosensors, and thus will not have an adverse effect onsignal-to-noise ratio. In addition, adjusting integration time toequalize signals, as in the present disclosure, requires less of thesignal range to be allocated to correction, which further enables ahigher signal-to-noise ratio.

The claims, as originally presented and as they may be amended,encompass variations, alternatives, modifications, improvements,equivalents, and substantial equivalents of the embodiments andteachings disclosed herein, including those that are presentlyunforeseen or unappreciated, and that, for example, may arise fromapplicants/patentees and others.

1. A photosensor chip, comprising: a first set of photosensors; acontrol portion for accepting an external integration signal, the signalcausing an integration time for the set of photosensors; a signaladjustor associated with the control portion, the signal adjustoreffectively altering the external integration signal to cause thecontrol portion to cause a modified integration time for the first setof photosensors.
 2. The chip of claim 1, wherein the signal adjustoreffectively causes the modified integration signal to be different fromthe external integration signal by a predetermined duration.
 3. The chipof claim 1, wherein the signal adjustor effectively causes the modifiedintegration signal to be different from the external integration signalby a predetermined proportion.
 4. The chip of claim 1, wherein,following manufacture of the photosensor chip, the signal adjustoraccepts a datum instructing the signal adjustor to modify the externalintegration signal in a predetermined manner.
 5. The chip of claim 4,wherein, following manufacture of the photosensor chip, the signaladjustor accepts a datum instructing the signal adjustor to cause amodified integration signal to be different from the externalintegration signal by a predetermined duration, the predeterminedduration being related to the datum.
 6. The chip of claim 1, furthercomprising a second set of photosensors; the control portion accepting asecond external integration signal, the second external integrationsignal causing an integration time for the second set of photosensors;and a second signal adjustor associated with the control portion, thesecond signal adjustor effectively altering the second externalintegration signal to cause the control portion to cause a modifiedintegration time for the second set of photosensors.
 7. The chip ofclaim 6, wherein the first set of photosensors is sensitive to a firstcolor and the second set of photosensors is sensitive to a second color.8. A photosensitive apparatus comprising: a plurality of photosensorchips, each chip including a first set of photosensors, a controlportion for accepting an external integration signal, the signal causingan integration time for the set of photosensors, and a signal adjustorassociated with the control portion, the signal adjustor effectivelyaltering the external integration signal to cause the control portion tocause a modified integration time for the first set of photosensors; anda first common line for applying a first external integration signal toeach of the plurality of photosensor chips.
 9. The photosensitiveapparatus of claim 8, further comprising a second common line forapplying a second external integration signal to each of the pluralityof photosensor chips, and each chip further including a second set ofphotosensors, the control portion of each chip accepting the secondexternal integration signal, the second external integration signalcausing an integration time for the second set of photosensors; and asecond signal adjustor associated with the control portion, the secondsignal adjustor effectively altering the second external integrationsignal to cause the control portion to cause a modified integration timefor the second set of photosensors.
 10. The apparatus of claim 9,wherein, for each chip, the first set of photosensors is sensitive to afirst color and the second set of photosensors is sensitive to a secondcolor.